The physical control layer contains information necessary to configure physical channel parameters at the receiving end of a wireless communication system. The control information needs to be decoded prior to the processing of the actual data samples composed of payload information provided by the higher layers. The control bits are either transmitted prior to the payload or in parallel. In general, to minimize the synchronization efforts and the size of latency buffers, and to reduce system throughput, the configuration, or reconfiguration of the receiver should be accomplished as fast as possible. Therefore, a latency constraint decoding and configuration problem should be addressed, where only a few bits, or control bits, are to be decoded as fast as possible.
The reliability of the control information should be guaranteed, since the remaining payload processing becomes obsolete in cases of erroneous control signaling. Error robustness can be guaranteed by adding redundancy to the control bits. Upon reception of the encoded control information, the receiver feeds the data into the corresponding decoder to recreate an exact copy of the originally transmitted control bits. The drawback is a considerable increase in processing complexity to implement the sophisticated algorithms. Moreover, the system designers can pick from various forward error correction techniques with different complexity and error correction characteristics. Forward error correction codes comprise linear block codes and convolutional codes.
The limited bandwidth of the air interface, coupled with the large amount of redundancy required to guarantee reliable transmission, limits the number of control bits to be transmitted. To further improve transmission reliability, a modulation scheme with advantageous distance properties among the different signal constellation points should be chosen. Simple modulation schemes such as BPSK (binary phase-shift keying) or QPSK (quaternary phase-shift keying) are ideal candidates for reliable transmission due to high SNR (signal-to-noise ratio) of adjacent symbols. However, with wireless systems becoming more and more complex, the need for smaller, faster and more power-efficient approaches is the key challenge of future system-on-chip designs.
Conventional approaches determine a sequence of bits from a reference sequence space comprising a large number of reference sequences, and that requires a correspondingly large memory size. Such a method is known in the art as maximum-likelihood sequence estimation (MLSE). Despite its exponential complexity, one key property of the MLSE decoding method is its inherent flexibility. That is, each sequence can be decoded in an optimal way no matter what encoding scheme was used. However, the MLSE decoding method requires a one-to-one mapping between the bits before and after encoding. As a result, it is necessary to unambiguously decode the sequence at the receiving side.